Technologies, Performance and Costs for Wastewater Nutrient Removal and Implementation Recommendations. Colorado Water Quality Control Division

Transcription

1 Technologies, Performance and Costs for Wastewater Nutrient Removal and Implementation Recommendations Colorado Water Quality Control Division November 2010

2 1.0 Background In support of the Water Quality Control Division s (Division) work in the development of numeric criteria for streams and reservoirs, the Division developed and issued a document entitled Technologies, Performance and Costs for Wastewater Nutrient Removal. The intent of the document was twofold: (1) to present the results of the Division s evaluation of previouslypublished information regarding performance, availability and cost of technologies that are likely to be applicable to publicly owned treatment works (POTWs) and other dischargers of nutrients; and (2) to present the Division s resulting perspective on the treatment technologies and the associated, expected performance and costs in light of the proposed draft numeric criteria. The document was released to the Colorado Water Quality Forum (Forum) Nutrient Criteria Workgroup on September 2, 2010 for review and comment, and the Division formally presented a summary of the information at the Workgroup s September 9, 2010 meeting. The Division received comments on the document from multiple members of the Workgroup. In considering the comments received, the Division re-evaluated the information that was included in the original document and initiated an expanded review of readily-available, published information regarding nutrient removal technologies and the primary, associated, considerations and issues. The purpose of this reissued version is to provide a summary of the Division s expanded review work and the associated conclusions to which the Division has come and to address the comments that were received on the original document. As was the case with the Division s original September 2, 2010 document, this reissued version is focused upon wastewater treatment facilities that are designed and intended to treat domestic sewage (publicly owned treatment works (POTWs) and non-public sewage treatment facilities). Treatment information common to industrial wastewater treatment facilities, such as air stripping, breakpoint chlorination, and ion exchange treatment processes, are not addressed in this report since the processes are generally found infeasible for POTWs due to cost, technical, or regulatory considerations (EPA, Mun. Nutr. Remov. Technol. 1: 2-1). Additionally, information regarding non-point source dischargers is excluded from this document as the topic is broad and is outside of the intended scope of this document. 2.0 Specific Considerations 2.1 Bioavailability Versus Recalcitrant Parameter Components Nitrogen Figure 1 illustrates the basic forms of nitrogen that are typically found within municipal wastewater and that may also be found in some industrial wastewaters. Nitrogen (total as N) mainly enters wastewater treatment facilities as ammonia and organic nitrogen, which includes both dissolved and particulate components (Tchobanoglous, Burton, and Stensel 186). While all of the influent ammonia and nitrate, where present, can theoretically be biodegraded through nitrification and/or denitrification processes, only a portion of the influent particulate and Page 2 of 25 December 6, 2010

3 dissolved organic nitrogen is biodegradable through hydrolysis of organic nitrogen to ammonia followed by nitrification and denitrification processes. Based on field data, about 40 to 60 percent of the influent dissolved organic nitrogen is biodegradable (Stensel 10). In theory, only recalcitrant forms of particulate and dissolved organic nitrogen should remain following biological treatment. The majority of the recalcitrant particulate organic nitrogen can be removed through physical separation processes leaving only the refractory dissolved organic nitrogen to be discharged with the wastewater effluent. In reality, treatment systems are subject to dynamic changes and are not 100 percent effective. Page 3 of 25 December 6, 2010

4 Figure 1: Forms of Total Nitrogen (adapted from WEF MOP- April 2010) Table 2 provides estimates based on various studies for the theoretical limit of technology that is available through a BNR treatment process. Table 2 Nitrogen Effluent Concentrations Following BNR Species Effluent Concentration Range, mg/l (Stensel 6) Treatment Technology Limit, mg/l (EPA, Bio. Nut. Rem. Proc. and Costs, 2) Technology Performance Characteristics, mg/l (EPA, Nut. Cont. Des. Man. 6-40) Percent of Total Nitrogen in Effluent Nitrate ~ % Ammonia ~ < % Particulate ~0.01 < % Organic Nitrogen Dissolved Organic % Nitrogen a Total Nitrogen % a - Organic nitrogen particles less than 0.45µm are considered to be dissolved While the theoretical limit of technology (LOT) for removal of dissolved organic nitrogen has an estimated range of 0.5 to 1.5 mg/l, field data collected from BNR process effluents throughout the United States reveal a range of effluent dissolved organic nitrogen of 0.10 to 2.80 mg/l with a median value of 1.2 mg/l (Stensel 7; Clark 1:4-14). Isolating specific data from 188 facilities in Maryland and Virginia, the study found that 65 percent of the facilities had effluent dissolved organic nitrogen values at 1.0 mg/l or less (Stensel 7). While this broad study Page 4 of 25 December 6, 2010

5 appears to provide a solid indication of the anticipated effluent dissolved organic nitrogen following BNR processes, the reference noted that wastewater treatment facilities receiving significant industrial contributions may encounter higher effluent concentrations of dissolved organic nitrogen (Clark 1: ). As can be seen from the field data and the theoretical values presented previously, the refractory dissolved organic nitrogen represents a significant portion of the effluent total nitrogen making low total nitrogen concentrations (< 2-3 mg/l) difficult to achieve with only biological nutrient removal processes that do not treat the refractory organic nitrogen. Potential treatment methods for the removal of the refractory dissolved organic nitrogen include expensive alternatives such as chemical oxidation or reverse osmosis. Chemical oxidation would require a subsequent biological treatment step to biodegrade the oxidation products (Stensel 10). The composition of refractory dissolved organic nitrogen is currently a topic of study, but it appears to consist of unidentified high molecular weight humic compounds with unknown structural characteristics (Stensel 7). Information regarding the biological availability of refractory dissolved organic nitrogen for uptake by algae and/or bacteria is not consistently represented by reference materials. One reference describes the refractory dissolved organic nitrogen s availability for uptake by algae or bacteria in the following paraphrased excerpts (Stensel 7, 11, 12, and 16): high molecular weight effluent dissolved organic nitrogen constituents are considered to be non-biodegradable or recalcitrant recalcitrant effluent dissolved organic nitrogen is that portion of the dissolved organic nitrogen that is considered not available for algal or bacterial growth over a time scale of days to weeks that represents the time of travel through the water area of interest not all of the effluent dissolved organic nitrogen from BNR treatment facilities is immediately bioavailable for algae and the recalcitrant effluent dissolved organic nitrogen fraction may vary for different receiving stream locations bioassay must provide a measurement of recalcitrant effluent dissolved nitrogen that would indeed be inert in the receiving water over an exposure time frame that is deemed appropriate A second reference describes the refractory dissolved organic nitrogen in the following ways (Clark 1:4-2): the portion of effluent dissolved nitrogen resistant to biological transformation and uptake by algae or other aquatic organisms in surface waters Page 5 of 25 December 6, 2010

6 the recalcitrant fraction of dissolved organic nitrogen is less important to the environment since it is not expected to encourage algal growth Based on the specific wording used in these references, the recalcitrant portions of the dissolved organic nitrogen do not appear to be categorically unavailable as suggested by the naming convention but, instead, become available for biological uptake under specific conditions or at a slower rate than other forms of nitrogen found in wastewater effluent. The biological availability of the refractory dissolved organic nitrogen may vary depending on conditions of the receiving stream (i.e. ph, light, temperature, salinity, etc.). While the fate of recalcitrant dissolved organic nitrogen in surface waters is a current topic of study, variations in how the recalcitrant dissolved organic nitrogen breaks down in a natural environment may pertain to both fresh water only systems and systems that include a combination of fresh water and salt water transitions (Stensel 11). At this time, a standard bioassay method has not been established to determine the biodegradability of organic nitrogen species (Clark 1: 4-2). A test protocol for performing water quality-based bioassays is being developed. The basics of the protocol include digestion of the sample with lab cultured algae and measurement of the dissolved organic nitrogen concentrations at specific intervals. While straight forward, key testing parameters are still being evaluated (Stensel 12-19) Phosphorus Figure 2 illustrates the basic forms of phosphorus typically found within wastewater treatment processes. Phosphorus (total as P) mainly enters wastewater treatment facilities as inorganic (i.e. orthophosphate and polyphosphate) and organic phosphate, which includes both dissolved and particulate components. From any starting form, phosphorus must be removed through treatment in particulate form either through biosolids wasting or physical separation processes (Clark 1:4-3). Orthophosphate forms are readily available for biological uptake whereas polyphosphates must be converted to orthophosphate forms through a slow rate hydrolysis process before becoming available for biological metabolism (Tchobanoglous, Burton, and Stensel 63-64). Theoretically, all influent inorganic phosphorus can be consumed through biological processes leaving only recalcitrant forms of particulate and dissolved organic phosphorus following biological treatment. The majority of the recalcitrant particulate organic phosphorus can be removed through physical separation processes leaving only the refractory dissolved organic phosphorus to be discharged with the wastewater effluent. Page 6 of 25 December 6, 2010

7 Figure 2: Forms of Total Phosphorus (modified from WEF-MOP, April 2010) In reality, treatment systems are subject to dynamic changes and are not 100 percent effective. Table 3 provides estimates based on various studies for the theoretical limit of technology that is available through a BNR treatment process. Table 3. Phosphorus Effluent Concentrations Following Various Treatment Scenarios Treatment Total Phosphorus Effluent Concentration Range, mg/l (Neethling 1) Total Phosphorus Effluent Concentration Range, mg/l (NACWA 4) Total Phosphorus Effluent Concentration Range, mg/l (EPA, Nut. Con. Design Man. 6-40) BNR Conventional Secondary Treatment with Chemical Addition BNR with Tertiary Chemical and Filtration Processes The middle two columns of Table 3 present the generally accepted achievable phosphorus treatment performance for various technology types. The rightmost column represents ranges extracted from the results of a study that examined the removal performance statistics for active full-scale wastewater treatment facilities throughout the United States. The concentration ranges represent the Reliably Achievable Performance in which 95 percent of the facility s effluent samples Page 7 of 25 December 6, 2010

8 were below the indicated value over a three year sampling period ((EPA, Nut. Con. Design Man. 6-40)). While the information appears to provide a reasonable range of total effluent phosphorus concentrations for domestic wastewaters, one reference indicated that industrial wastewater treatment facilities may not be able to reach these numeric effluent ranges for total phosphorus due to higher influent levels which may contain larger fractions of refractory dissolved organic phosphorus (Clark 1: 3-7). A site specific study at the Coeur D Alene, Idaho wastewater treatment plant, that receives primarily domestic waste, identified a typical refractory dissolved organic phosphorus effluent concentration between and mg/l following four different physical/chemical treatment options (Neethling 5). When compared against the bottom row of total phosphorus ranges shown in Table 3, the refractory dissolved organic phosphorus effluent concentration from the Coeur D Alene facility would account for approximately percent of the effluent total phosphorus. Wastewater effluents likely include less than 0.01 mg/l of soluble organic phosphorus; however, as effluent requirements decline, this fraction becomes increasingly significant (Neethling 7). Understanding phosphorus speciation may be critical for enhancing removal efficiencies at wastewater treatment facilities as speciation is an important area of current research especially for biodegradability and availability for biological uptake. The composition of refractory dissolved organic phosphorus is currently a topic of study, but it appears to consist of organic phosphorus and possibly other complexed phosphorus compounds (Clark 1:4-5). Another source indicates that non-reactive phosphorus constituents are not known, but may contain polyphosphates, condensed phosphates, and dissolved organic phosphorus species. The information regarding the ultimate biological availability of refractory dissolved organic phosphorus is not well defined. The following paraphrased excerpts were taken from various references: Environmental impacts of refractory dissolved organic phosphorus have not been established. Similarities could exist between the refractory dissolved organic phosphorus and the refractory dissolved organic nitrogen in terms of the types of compounds, significance, and environmental fate and impact. The biodegradation and the biological availability of the refractory dissolved organic phosphorus remain in question (Neethling 6) Effluent dissolved phosphorus is better characterized as non-reactive with two subclasses, bioavailable and recalcitrant (Clark 1: 4-5). Bioavailable dissolved organic phosphorus assimilates in surface waters through bacteria and algae uptake. This fraction is of importance in the environment since it will support algal growth. Page 8 of 25 December 6, 2010

9 Recalcitrant dissolved organic phosphorus is resistant to biological transformation and uptake by algae and bacteria in surface waters. This fraction is of less importance to the environment since it is not expected to encourage algal growth. Based on the specific wording used in these references, the recalcitrant portions of the dissolved organic phosphorus do not appear to be categorically unavailable as suggested by the naming convention, but instead, may become available for biological uptake under specific conditions or at a slower rate than other forms of phosphorus found in wastewater effluent. The biological availability of the refractory dissolved organic phosphorus may vary depending on conditions of the receiving stream (i.e. ph, light, temperature, salinity, etc.). Recalcitrant phosphorus may act similarly to refractory nitrogen in a natural environment where some fraction of the recalcitrant phosphorus may become bioavailable. At this time, current treatment processes do not appear capable of removing this refractory phosphorus component, except for possibly RO (Clark 1:4-24). At this time, Standard Methods does not have a method for directly determining total organic phosphorus, total non-reactive phosphorus, dissolved organic phosphorus, or dissolved non-reactive phosphorus. These values can be calculated by testing other phosphorus fractions (Clark 1: , 4-28). 2.2 Averaging Period Limits for Nutrients According to information provided by WERF (Clark 127), nutrients are different from conventional and toxic parameters as they have no direct or immediate impact on water quality. Additionally, it is indicated that the exposure period for nutrients is longer than one month and may be up to a few years, and the average exposure rather than the maximum is of concern. An important consideration in the evaluation and discussion of nutrient removal technology capability and feasibility is therefore the associated compliance period (i.e. averaging period limit) that will be included in discharge permits. The decisions that are made with regard to the averaging period limits that will be set for nutrients in Colorado will ultimately dictate the needs (for all types and sizes of facilities) with regard to technology selection and overall associated costs. Because of the nature of nutrients, consideration should be given to averaging period limits different from the typically-applied (per NPDES, 40 CFR (d)) average monthly, average weekly and maximum daily limits that exist for conventional and toxic parameters. This consideration of averaging period limit is intrinsic to the concepts presented throughout the remainder of this paper. Another related, but different concept of note is that of seasonally-applied effluent limits. As is the case with the averaging period limits, seasonally-applied limits will impact facility needs with regard to technology selection and overall associated costs. Page 9 of 25 December 6, 2010

10 2.3 Operator Capacity in Colorado Although somewhat outside of the scope of this document, the topic of operator capacity has direct bearing on treatment technology considerations and is therefore briefly addressed here. Colorado, like many other states, is facing a shortage of properly trained and certified operators. As such, this issue becomes even more concerning when considering treatment technologies for nutrient removal, which typically require increased attention to multiple process parameters (depending on the technology), increased instrumentation, automation and operators who can operate these increasingly more sophisticated facilities. Impacts on facility certification levels are likely as well. Because of these factors, it is important that operator capacity is considered simultaneously with technology capabilities. 3.0 Theoretical Limit of Specific Technologies versus Actual Treatment Capabilities The term limits of technology, also referred to as the technologically achievable limit, for the purpose of this paper, refers to the absolute capability that a particular treatment process or set of treatment processes can achieve under advantageous conditions. While the limit of technolgy provides some insight in the selection of a particular treatment technology, it is not appropriate for making determinations regarding actual treatment capability as most facilities do not operate at the LOT due to environmental and operational variability. As such, the Division s research with regard to nutrient removal technology capabilities necessitated consideration of an approach other than the LOT. The Division found two statistical methods that have been applied to enable the evaluation and comparison of nutrient-removal treatment processes, taking into consideration the differing environmental and operational conditions. These two methods are Technology Performance Statistics (TPS) and Coefficient of Variation. While both methods rely upon performing statistical analysis on field data, TPS expresses reliability through three factors and the Coefficient of Variation method measures reliability through the coefficient of variation term one standard deviation divided by the mean, expressed as a percentage (EPA, Nut. Cont. Design Man. 6-37; EPA, Mun. Nut. Rem. Technol. Vol. 2. B-1). 3.1 Technology Performance Statistics Technology Performance Statistics (TPS) has been used to define the performance of a particular treatment or set of treatment processes through frequency and reliability. The performance is tied to a statistical rank used to express the probability of achieving a certain performance (Clark 1:4-16). TPS takes into account the conditions at the time of data collection, which might include process configurations, treatment objectives, existing versus design loadings, solids handling processes, seasonality, solids residence times, industrial loadings, and other critical environmental conditions (EPA, Nut. Cont. Design Man. 6-37). Essentially, the TPS brackets the ranges of effluent concentrations found at various types of well-operated and maintained wastewater treatment facilities. Page 10 of 25 December 6, 2010

11 The TPS system uses three levels to define achievable performance including Best Achievable Performance (TPS-14d), Average Process Performance (TPS-50%), and Reliable Processes Performance (TPS-95%). The following paraphrased definitions for the three performance levels were taken from the Water Environment Research Federation (Clark 1: ) and the United States Environmental Protection Agency (EPA, Nut. Cont. Design Man. 6-37): Best Achievable Performance (TPS-14d) the lowest concentration (best sustained performance) observed over a 14-day period for conditions experienced at the treatment plant. The value represents either the lowest running 14-day average or calculated 3.84 th percentile from all data. The facility exhibits weaker performance 50 weeks per year. Average Process Performance (TPS-50%) the concentration achieved on a statistical annual average basis under operating conditions. The facility exceeds the average process performance half of the time. Reliable Process Performance (TPS 95%) the effluent concentration reliably achieved 95 percent of the time. This measure is exceeded three times, when determined monthly, in a five year period. Based on the available literature, the TPS process has been applied to data from at least five overlapping national wastewater treatment plant studies from some of the nation s strongest-performing nutrient removal wastewater treatment plants (Clark 1: ). The best performing wastewater treatment plants were used to demonstrate the abilities of treatment with proper operations and maintenance support (EPA, Nut. Cont. Design Man. 6-37). With all the compiled data, the study identified the following notable trends and performance data for various levels of nutrient treatment processes: When comparing TPS performance indicators from multiple data sets gathered at a single wastewater treatment facility, the information showed that the TPS-50% remained relatively similar compared to the TPS-95% which showed considerable variation (Clark 1:4-20). Data provided for 18 wastewater treatment facilities indicated that nearly all the facilities maintained total nitrogen concentrations less than 4 mg/l and all but one facility maintained effluent total nitrogen concentrations less than 6 mg/l. Most facilities relied on tertiary filtration with two-thirds adding an additional nitrogen source for enhanced denitrification following varying secondary treatment technologies (Clark 1:4-20). The data indicated that best achievable performance for total nitrogen is typically 40 to 70 percent of the average process performance, and the reliable performance is 1.5 to 2.5 times higher than the average performance (Clark 1:4-22). Data provided for 52 wastewater treatment facilities indicated that all facilities maintained total phosphorus effluent concentrations less than 1.0 mg/l with nearly Page 11 of 25 December 6, 2010

12 two-thirds achieving effluent total phosphorus concentrations less than 0.1 mg/l. All facilities provided tertiary treatment following varying secondary treatment technologies (Clark 1:4-24). Significant total phosphorus removal depends on complete removal of particulate phosphorus species (Clark 1:4-24). The data indicated that best achievable performance for total phosphorus is typically 40 to 60 percent of the average process performance, and the reliable performance is 1.5 to 4 times higher than the average performance (Clark 1:4-25) Facilities simultaneously removing nitrogen and phosphorus through BNR processes face greater challenges with the balance of available nutrients and treatment conditions. The data demonstrated that nitrogen and phosphorus removal trended oppositely meaning that as a facility achieved a higher degree of treatment for one nutrient, the level of treatment declined for the other (Clark 1: ). While the TPS study provides a statistical evaluation of process performance, the study did not specify technology limits based upon treatment technologies. As a point of interest, the Division attempted to ascertain how the relationship between the various performance indicators for total nitrogen and phosphorus compared to published treatment ranges for limit of technology or other similar markers. The first step in this process was to compile documented limit of technology or other similar treatment technology markers regarding total nitrogen and total phosphorus from available references. The limits and other similar markers were categorized into bins representing general treatment types. Data within each bin was further divided specific to nitrogen and phosphorus. Most pertinent reference data was considered comparable to reliable process performance (TPS-95%). This data is provided in Table 4. During the second step, the Division identified the highest concentration from the references, and established this value as the reliable process performance (TPS-95%). The Division then applied the general relationships between TPS-95%, TPS-50%, and TPS-14d established during the TPS studies to calculate the TPS-50% and TPS-14d ranges for nitrogen and phosphorus in each treatment bin. The results correlated well with generally accepted limits of technology. For example, well-operated BNR facilities (bin 3 or 4) are expected to reliably achieve an effluent total phosphorus concentration of 1 mg/l and may produce total phosphorus concentrations around 0.5 mg/l. According to the concentration ranges calculated by the Division for TPS-50% and TPS-14d, the treatment process should be able to produce and average process performance and best achievable performance for total phosphorus of 0.7 and 0.4 mg/l, respectively. These values correlate well with expected results. Nitrogen treatment comparisons provide similar results. The strong correlation between well-published, reliable process performance limits and the general relationships between TPS-95%, TPS-50%, and TPS-14d may help in the Page 12 of 25 December 6, 2010

13 development of reasonable numeric effluent limits and associated averaging periods for nutrients. Longer averaging periods based upontps-50% performance would provide systems more flexibility to ensure permit compliance for nutrients. This concept has some merit considering that nutrients are not acute toxins like metals, but rather affect aquatic ecosystems on a chronic and/or seasonal basis. 3.2 Coefficient of Variation Similar to the TPS, the coefficient of variation (CV) can be a measure of a specific treatment process reliability to meet treatment objectives. The CV is a single term that represents any sampled parameter, expressed as the percentage of one standard deviation divided by the average, for any defined data averaging period (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol. 2. B-1). One standard deviation from the mean (plus or minus) defines a subgroup of data such that all measured values within the upper and lower brackets represent 68 percent of all measurements. In turn, dividing the standard deviation by the mean normalizes the data so that different data sets can be compared without having to be understood in the context of the mean. For this discussion, the coefficient of variation represents treatment process reliability. A higher CV represents a wider range of sample values and a lower CV represents a narrower range of sample values. When applied to effluent TN, a high CV means that the effluent TN value varies significantly for a particular treatment process analyzed over specific time scale (i.e. annual, monthly, weekly, daily, etc.). While intended as a way for systems to evaluate and choose an appropriate treatment technology that can reliably meet defined numeric nutrient criteria, the CV can also be used to evaluate how to best set technology-based effluent limits. If all available treatment systems used for BNR have high CV values as they relate to data for TN and TP, implementation of associated numeric nutrient criteria would need to provide for longer averaging periods to account for the variability. Alternately, if all available BNR treatment systems exhibit low CV values, implementation of associated numeric nutrient criteria could involve shorter averaging periods. The EPA performed a nutrient treatment study of 30 full-scale wastewater treatment facilities nationwide to establish reliability of BNR treatment processes using the CV technique. Tables 5, 6, and 7 illustrate the results from the EPA study for total nitrogen, total phosphorus, and total nitrogen and total phosphorus treatment systems, respectively (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol. 1. ES-3, , , , 3-43). The tabulated data categorize each treatment process based on its ability to reliably meet a specified average total nutrient limit (i.e. 3, 5, 10 mg/l). Each treatment process is further classified by a standard deviation and CV. While the systems may fall into a specified average total nutrient limit, CV values for treatment systems within a specific annual average limit range vary dramatically. For example, within the nitrogen specific table under a TN of 5, the SBR treatment system recorded an annual average of 4.59 mg/l TN with a CV of 50; the MLE treatment system recorded and annual average of 4.35 mg/l TN with a CV of 23. Based on this analysis, both treatment system could meet an average annual effluent limit of 5 mg/l TN, but only the MLE system would Page 13 of 25 December 6, 2010

14 have the ability to reliably meet more stringent monthly, weekly, or daily effluent limits due to a lower CV rating. The CV data provided by this study may be useful in the development of reasonable effluent averaging periods and daily maximums. While informative, the data from the EPA should be used only after rigorous deliberation. The data may be used as a guide, but does not holistically relate to conditions found within Colorado. For example, only two (2) of the facilities listed typically record wastewater temperatures below 14 degrees Celsius whereas many Colorado facilities routinely experience wastewater temperatures below this level. In addition, reliability at most facilities may be improved through operational practices or system reconfiguration; therefore, the identified CVs are not absolute for all similar treatment technologies (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol ). Page 14 of 25 December 6, 2010

15 Table 4. Technology Performance Statistics by Treatment Bins Typical Treatment Processes Level of Treatment for Nitrogen Level of Treatment for Phosphorus Bin Associated Treatment Types Lagoon Activated Sludge Target Treatment BOD, TSS, incidental N & P BOD, TSS, incidental N & P Typical Liquid Stream Treatment Processes Typical Treatment Processes aeration, sludge settling, chlorination, dechlorination Multi Cell Aerated Lagoon; Facultative Lagoon screening; 1 solids separation; aerobic; 2 solids separation; chlorination; dechlorination Activated Sludge BNR or EBNR with Chemical Addition and Reverse Osmosis (RO) or Ultra Filtration (UF) Biological Nutrient Removal (BNR) Enhanced Biological Nutrient Removal (EBNR) BNR or EBNR with Chemical Addition BNR or EBNR with Chemical Addition and 3 Filtration BOD, TSS, TN, TP (Typically TN or TP) BOD, TSS, TN, TP BOD, TSS, TN, TP BOD, TSS, TN, TP BOD, TSS, TN, TP screening; 1 solids separation; single stages of anaerobic, anoxic and aerobic zones; 2 solids separation; chlorination; dechlorination MLE; Sequencing Batch Reactor (SBR); IFAS; MBBR; Ludzack Ettinger; Wuhrman; Bardenpho (3 or 4-stage); RBC; Trickling Filter screening; 1 solids separation; multiple stages of anaerobic, anoxic and aerobic zones; 2 solids separation; chlorination; dechlorination Bardenpho (5-stage); UCT; VIP; Johannesburg; SBR; Phoredox (AO); 3-stage Phoredox (A2O) screening; 1 solids separation; multiple stages of anaerobic, anoxic and aerobic zones; 2 solids separation; chemical addition in 1 or 2 solids separation; chlorination; dechlorination Any processes in Bins 2 or 3 with additional chemical addition within the process for removal of TP screening; 1 solids separation; multiple stages of anaerobic, anoxic and aerobic zones; 2 solids separation; chemical addition with 3 media filtration; chlorination; dechlorination Any processes in Bins 2 or 3 with additional chemical addition within the process for removal of TP with 3 media filtration (WERF, 2008) ~ ~ 10 mg/l 3 mg/l ~ ~ ~ (EPA, 2007) ~ ~ 6-12 mg/l (Small System) 3-5 mg/l; ~ ~ ~ (WERF, 2010) ~ mg/l 10 mg/l 4-6 mg/l ~ 3-4 mg/l 1 mg/l (EPA, 2010) ~ ~ 5-8 mg/l 3-5 mg/l ~ ~ ~ screening; 1 solids separation; multiple stages of anaerobic, anoxic and aerobic zones; 2 solids separation; chemical addition with 3 RO or UF membrane filtration; chlorination; dechlorination Any processes in Bins 2 or 3 with additional chemical addition within the process for removal of TP with 3 RO or UF Reliable Process Performance (TPS-95%) ~ 30 mg/l 10 mg/l (12 mg/l for small system) 6 mg/l ~ 4 mg/l 1 mg/l Calculated Average Process Performance (TPS-50%) mg/l mg/l mg/l mg/l Calculated Best Achievable Performance (TPS-14d) mg/l mg/l mg/l mg/l (WERF, 2008) ~ ~ ~ mg/l mg/l mg/l ~ (EPA, 2007) ~ ~ ~ ~ ~ 0.15 mg/l ~ (WERF, 2010) ~ 4-6 mg/l 1 mg/l mg/l ~ mg/l 0.01 mg/l (EPA, 2010) ~ ~ ~ mg/l mg/l mg/l ~ (EPA, 2007) ~ ~ ~ 0.2 mg/l ~ ~ mg/l Reliable Process Performance (TSP-95%) ~ 6 mg/l 1 mg/l 1 mg/l 0.65 mg/l 0.36 mg/l 0.07 mg/l Calculated Average Process Performance (TPS-50%) mg/l mg/l mg/l mg/l mg/l mg/l Calculated Best Achievable Performance (TPS-14d) mg/l mg/l mg/l mg/l mg/l mg/l Page 15 of 25 December 6, 2010

16 Table 5. Process Performance Data: Nitrogen Removal Plant Effluent (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol ) Plant effluent observed value or range (mg/l) Nitrogen removal Variability (mg/l) Annual Max. month average (50%) (92%) Max. week (98%) Max. day (99.7%) Reference TN (ppm) Technology Std dev./ CV-% 10 Johannesburg 2.03 to / Hagerstown, Maryland A2O 7.3 to 9.0 a Maryland Report b VIP 6.12 a Neethling 2005 Step-feed AS 1.80/ Cumberland, Maryland 5 IFAS 4.9 to 11.3 a Masterson 2004 McQuarrie 2004 MBBR 5.8 to 6.8 a Täljemark et al MLE 2.2 to 15 a Leesburg Westminster, Maryland 1.00/ stage Bardenpho 3.5 to 12.1 a Maryland Report Schreiber system 8 a Maryland Report Blue Plains process 7.5 a Washington DC c (Kang et al. 1992) (Sadick et al. 1998) PIDs, clarifiers, aerobic 1.8 to / North Cary, North Carolina d digestion PIDs 1.4 to / Jewett City, Connecticutc SBR 1.6 to / Thomaston, Connecticutc Cyclic on-off 3.1 to / Ridgefield, Connecticutc Westbank 2.7 to / Kelowna, British Columbia c,d Step-feed AS 3.7 to / Fairfax, Virginiac, d 3 Biological aerated 1.4 to / e 7.13 e 9.80 a a Cheshire, Connecticut c filters Concentric oxidation 1.6 to / Hammonton, New Jersey ditch Step-feed AS 1 to / Piscataway, Maryland c Notes: A 2 O = anaerobic/anoxic/oxic AS = activated sludge CV = coefficient of variation IFAS = integrated fixed-film activated sludge MBBR = moving-bed biofilm reactor MLE = modified Ludzak-Ettinger PID = phased isolation ditch SBR = sequencing batch reactor VIP = Virginia Initiative process Performance periods are listed in Attachment at end of References section. a Data obtained from literature; data were not reviewed as part of project. b George Miles & Buhr, LLC, and Gannett Fleming c Retrofit application. d Case study plant is explained in more detail in Chapter 3. e Values are based on 8 months of data, rather than 12 months. f Clearwater, Florida, has two facilities Marshall Street (MS) and Northeast (NE) The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plant loadings compared to their design at these facilities. Thus, they do not necessarily represent optimum operation of the technologies presented. 5-stage Bardenpho 1.24 to / / Clearwater, Florida-MS d,f Clearwater, Florida-NE f Denitrification filters 0.47 to / Johnston County, North Carolina c,d Denitrification filter 0.13 to / Lee County, Florida d Denitrifying activated 0.4 to / Western Branch, Maryland d sludge Page 16 of 25 December 6, 2010

17 Table 6. Process Performance Data: Phosphorus Removal Plant Effluent (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol ) TP (ppm) 2 1 Technology Range of values observed (mg/l) Std dev./ CV-% Phosphorus removal Variability (mg/l) Annual average (50%) Max. month (92%) Max. week (98%) Max. day (99.7%) Reference A2O with VFA addition, chemical addition, tertiary to / Durham, Oregon d clarifier, and filtrationa 0.5 VIP 0.19 to 5.0 c VIP, Neethling 2005 A/O 0.03 to / Genesee County, Michigan d UCT with filter 0.3 c Westbank with fermenter and filters 0.1 Chemical addition and flocculating clarifiers Penticton, British Columbia Barnard, to / Kelowna, British Columbia b,d 0.07 to / Chelsea, Michigan Truckee Meadows, Nevada Barnard et al PhoStrip < 0.1 Ortho- P c Modified UCT with fermenter 0.03 to / Kalispell, Montana Tertiary clarifier with chemical addition and filtersa to / McMinnville, Oregona A/O with chemical addition to filters 0.03 to / Clark County, Nevada b Step-feed AS with fermenter and filter 0.02 to / Fairfax, Virginia b,d MBR to / Hyrum, Utah Denitrification filter with alum 0.02 to / Lee County, Florida b 5-stage Bardenpho oxidation ditch with chemical addition and filters 0.02 to / Pinery Water, Colorado MBR 0.01 to / Lone Tree Creek, Colorado Notes: A 2 O = anaerobic/anoxic/oxic AS = activated sludge CV = coefficient of variation IFAS = integrated fixed-film activated sludge MBBR = moving-bed biofilm reactor MLE = modified Ludzak-Ettinger PID = phased isolation ditch SBR = sequencing batch reactor VIP = Virginia Initiative process Performance periods are listed in Attachment at end of References section. a Data obtained from literature; data were not reviewed as part of project. b George Miles & Buhr, LLC, and Gannett Fleming c Retrofit application. d Case study plant is explained in more detail in Chapter 3. e Values are based on 8 months of data, rather than 12 months. f Clearwater, Florida, has two facilities Marshall Street (MS) and Northeast (NE) The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plant loadings compared to their design at these facilities. Thus, they do not necessarily represent optimum operation of the technologies presented. EBPR with high rate solids contact clarifier, chemical addition, and filters Chemical addition, tertiary clarifiers, filter, infiltration basin to 0.02 c Breckenridge, Colorado 0.01 (monthly averages) --0/ Brighton, Michigan Page 17 of 25 December 6, 2010

18 Table 7. Process Performance Data: Nitrogen and Phosphorus Removal Plant Effluent (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol ) Nitrogen and phosphorus removal Notes: Variability (mg/l) P (ppm) Std dev./ Annual Max. Max. Max. day Reference N (ppm) Technology Range of values observed (mg/l) CV-% average (50%) month (92%) week (98%) (99.7%) 10 Johannesburg TN: 2.03 to / Hagerstown, Maryland TP: 0.19 to / UCT TN: 8.9 to 10 a WEF and ASCE 2 TP: IFAS TIN: 5.6 to 11.3 a TP: 0.2 to 1.7 a Broomfield, CO McQuarrie 2004 VIP VIP with VFA addition Step-feed with fermenter Biodenipho/PID Modified UCT with VFA addition High rate, nitrification, and denitrification activated sludge 5-stage Bardenpho with chemical addition for P removal TN: 3 to 10 TP: 0.19 to 5.75 TN: 5 to 10 TP: 0.6 to 0.8 TN: < 5.0; 3 to 13 TP: < 0.3; 0.1 to 5 TN: 1.78 to 7.02 TP: 0.09 to / / / / TN: 5 to 6 a TP: 0.1 to 2.7 a TN: 0.4 to 10.4 TP: 0.05 to 1.88 TN: 1.24 to 4.29 TP: 0.06 to 0.37 TN: 0.87 to 5.59 TP: 0.06 to / / / / / / Rabinowitz 2004 Neethling 2005 Piscataway, MD North Cary, NC b 0.5 McDowell Creek, NC Neethling Western Branchb Hyattsville, MD Clearwater, FL-MS b Clearwater, FL-NE IFAS = integrated fixed-film activated sludge PID = phased isolation ditch UCT = University of Cape Town process VFA = volatile fatty acids VIP = Virginia Initiative process Performance periods are listed in table at end of References section a Data obtained from literature; data were not reviewed as part of report. b Subject of case study described in Chapter 3. c Retrofit application. The data reflect specific operating philosophy, permit limitations, influent conditions, flow conditions and the relative plant loadings compared to their design at these facilities. Thus, they do not necessarily represent optimum operation of the technologies presented. Denitrification filters with chemical addition TN: 0.13 to 6.50 TP: 0.02 to / / Fiesta Village b Lee County, FL Denitrification filters with chemical addition TN: 0.84 to 3.13 TP: 0.1 to / / Johnston Co., NC b,c Page 18 of 25 December 6, 2010

19 4.0 Economics Overview of Cost Information Advanced wastewater treatment processes capable of removing TN and TP have associated economic and environmental costs. Nutrient removal requires supplemental treatment facilities beyond those required for secondary treatment which increases capital, operations, and maintenance costs. Evaluating widespread cost impacts of implementing numeric nutrient criteria is complex. The Division considered the following cost studies as a representation of available data: Cost and Performance Evaluation of BNR Processes, 1998 Municipal Nutrient Removal Technologies Reference Document (Volumes 1 and 2), 2010 Biological Nutrient Removal Processes and Costs, 2007 Nutrient Management: Regulatory Approaches to Protect Water Quality Volume 1 Review of Existing Practices, 2010 Nutrients Issue Paper, 2009 While these references present extensive cost analyses, the data may not be directly applicable to the sizes and types of facilities that are found in Colorado and other important factors, such as material, labor, etc. may be different (from those in the data) as well. Many site-specific variables exist making each cost evaluation similar to, yet unique from, cost evaluations of all other nutrient process upgrades (NACWA 25). Additionally, many of the variables are interrelated causing ambiguity during site to site comparisons when the all site conditions are unknown or do not match. The Division considered the data presented and identified common issues within the references that would impact the direct application of the cost data to Colorado. The following list identifies and discusses some of the primary variables related to the challenges of generalizing unit costs associated with nutrient removal: Variable Impact on Cost Evaluations Cost Index: Economic Climate: Influent Characteristics and Discharge Limits: References generally use nationwide wastewater treatment facility data to develop cost per million gallon costs for upgrades and retrofits. While useful for establishing cost ranges, costs for materials, labor, and shipping vary by region and sometimes within regions. For example, the cost to mobilize for a construction project varies significantly within Colorado. Remote mountain areas may pay a premium compared to Front Range communities. While cost comparisons for different years can be somewhat normalized through cost indices, the economic climate can have a significant impact on capital costs through specific items such as supplier and contractor profit margins. Comparing cost studies performed in various years becomes troublesome as the economic climate varies nationwide as well as regionally. Influent wastewater characteristics impact the size and types of nutrient removal processes employed which translate into significant impacts on unit costs. Cost comparisons do not appear to address process sizing or chemical dose variations Page 19 of 25 December 6, 2010

20 Variable Impact on Cost Evaluations due to the influent wastewater characteristics to achieve specific discharge limits. Inclusions: Real Estate: Labor: Retrofits and New Construction: Cost studies often caveat cost per million gallon ranges by indicating that a particular item was included for one facility, but not another in the development of a unit cost range. For example, the EPA Municipal Nutrient Removal Technologies Reference Document provides a comparison of the operations and maintenance costs specific to nitrogen removal for three facilities. Within the discussion, the reference cautions that the cost per million gallon (MG) includes labor with the operations and maintenance costs for some facilities and not for others. The resulting cost per million gallon of wastewater treatment ranged from $63 to $136. The highest and lowest costs did not include labor in the operations and maintenance costs while the intermediate value did include labor (EPA, Mun. Nut. Rem. Tech. Ref. Doc. Vol. 1. ES-17). While helpful, the data does not provide a tiered cost enabling systems to infer that a higher unit cost includes labor. While real estate may also be considered as part of the Inclusions category, this variable received its own discussion since real estate purchases are not required by all facilities to install BNR. This site specific cost sometimes appears in reference studies as part of capital costs associated with advance treatment. Land purchase is site specific; costs vary widely and cannot be normalized easily. Labor costs vary regionally for both unionized and non-unionized skills. Additionally, studies do not specify whether labor includes both unionized and nonunionized labor forces which may impact the unit costs ranges for advanced treatment estimates. Additionally, labor typically employed at a wastewater treatment facility may perform expanded duties to address BNR facilities. The percentage of work associated with existing operations and maintenance staff at a BNR facility is undocumented and not well represented in the available data. Many references attempted to extract labor from the unit costs associated with BNR, but as seen from the Inclusions discussion, extraction of labor was not always possible and can blur the resulting unit cost range. While a few of the references address retrofit costs versus new construction for BNR, the data does not normalize well. As discussed in the Influent Characteristics and Discharge Limits section, site specific variable may dictate the type and size of treatment which directly impacts costs. Likewise, the inclusion of land and labor may impact the unit cost range. Additionally, information in references does not always fully disclose the starting point for upgrades. For example, upgrading an MLE process to a BNR may require the addition of anoxic and anaerobic zones while upgrading an SBR to a BNR process may only require the addition of an anaerobic zone with recycle modifications. These may result in a similar BNR, but the beginning point has an obvious impact on the overall capital cost. While direct comparisons of this type may be occurring in the references, comparing these two scenarios does not appear equivalent. Page 20 of 25 December 6, 2010